Method of preventing erosions and perforations in metal containers



Patented Nov. 2, 1937 omen STATES METHOD OF PREVENTING EROSIONS AND PERFOR-ATIONS IN METAL CONTAINERS Clauss Bur-kart Strauch, New York, N. Y.

No Drawing. Application May 29, 1936, Serial No. 82,623

8 Claims.

This invention relates to a method for preve'nting erosions and perforations in metal containers such as tin or tinned cans, collapsible tin tubes or the like, which are used for storing liquids or semi-liquid materials. More particularly the invention relates to the protection of metallic receptacles which have been provided with a protective coating of such type as will increase the tendency to perforations.

10 It 1 known to manufacturers using metallic containers for the packaging of foods, creams, jellies and the like, that these substances may in time and under certain conditions as for instance, prolonged hot weather, enter into reactions with the metal of the container and this will result in discoloration and other changes of the contents and in corrosion, pitting and even perforations of the container. The free acids and alkalies present in the contents most frequently cause the reaction with the metal, by forming metallic salts with the same. The reaction may also liberate hydrogen gas in such quantities that the container will take on a swollen appearance, known as a hydrogen swell.

2 These destructive reactions result most readily from contact with reactive metals such as iron, copper, lead and aluminum, and of the low priced metals less easily with tin. This accounts for the wide use of tin for containers either in pure form 30 as in collapsible tin tubes or as a coating such as in tinned cans. Even tin containers, however,

\ will enter into reactions with a great number of contents and may show all the reactive changes described above.

35 To overcome these difliculties, manufacturers of tin cans as well as ofcollapsible tin tubes, have coated the inner surfaces of the containers with alkali or acid resisting coatings, which are to prevent contact between contents and metal 40 of the container.

It was found however that in time any unprotected part of the metal which was accidentally not coated due to the presence of air bubbles or dust was corroded to a greater extent than the 45 container as a whole would have been, if no coating was used. The corroded spots, in certain products, frequently lead to perforations in such imperfectly coated containers, while the uncoated containers would show a degree of spoilage 50 but not the obvious perforations.

It is known that the tendency to perforations in coated tin cans has been overcome by the use of two or even three protective coats, which insure a the complete covering of the metal. This method,

5. however, is expensive and unsuitable for collapsible tubes, since the multiple coats impart undesired stifiness to the walls of the tubes, tend to obstruct the'neck of the tube, hinder proper-closing and sealing and add a prohibitive expense to the cost.

Furthermore, multiple coatings are not possible for collapsible tubes coated with petrolatum as described in my U. S. Patent 2,016,060, dated Oct.

1, 1935, since the coating is to be applied hot and will melt and fully remove any similar coating pre- 10 viously applied. The coating using petrolatum is of special importance for dual tubes, that is one tube within another, where it protects the inner tube from the contact with .the alkali content on one side and the acid content on the other, as 5 used in practice, and serves the purpose at the same time of sealing the openings of inner and Outer tubes, and securely prevents a premature contact between the two incompatibles stored. Such dual tubes, one storing an acid and one an alkaline formula both reactive to tin, are liable to violent reactions and formation of gas if the two incompatibles are united even through a pinhole. Such tubes are, therefore, in special need of a protective coating such as petrolatum, and must also be safeguarded against perforations, which are not prevented but rather favored by the soft and vulnerable petrolatum coating used.

It is a generally accepted fact that an acid jelly stored in an uncoated tin tube will react with the tin forming in time acid tin salts. This formation will continue until a saturation point or equilibrium has been reached, the entire contents reacting with all of the inner surface'of the container. I

I have found that in imperfectly coated containers the same reactive forces will take place, the entire contents, however, reacting against a. small exposed area of the metallic container only, which results in perforations before the contents 40 aresaturated and an equilibrium is reached.

I have, therefore, invented a novel method of protecting metal containers, coated oruncoated, by adding to the contents metallic salts in amounts up to the saturation point, such as would be formed in time from natural reactions between the contents and metallic container. I have found that the presence of such metallic salts will great- 13 retard the reaction of the contents with the container, since the contents are more or less saturated with those metallic salts that could be formed from the container. The acids and alkalies present in the contents have been found by me to be made substantially inactive towards the metal of the container, by their previous saturation with the metallic salts.

I have found that while my method is applicable to iron, lead or aluminum containers when using the corresponding metallic salts of those metals, it is best suited for use with containers consisting of tin or having a tinned surface when the contents are saturated before packing with tin salts. This is explained by the limited solubility of the tin salts formed by natural reaction in tin containers, which permits a close saturation of the contents with relatively small amounts of harmless and colorless tin salts.

With the foregoing objects outlined and with other objects in view which will appear as the description proceeds, the invention consists in the novel features hereinafter described in detail, and more particularly pointed out in the appended claims.

Acid products as packed in tin containers, contain generally a complex variety of weak acids such as fruit acids, gum acids, acetic acid, lactic acid, or the like. The same, but to a lesser degree, is true of alkaline products. Correspondent tin salts would be expensive if at all commercially available, and they are generally practically insoluble. Furthermore, it would require difiicult analyzing work to adapt the tin salts to be added, to the complex and changing active ionic compounds present in the natural products.

According to my invention I prefer to form the required tin salts within the batches of materials to be packed. In its simplest form this is done by adding metallic tin in the form of shredded foil or in colloidal state either to the whole batch or to its active constituents before they'are mixed with the other constituents of the batch. I prefer to accelerate the reaction by heat. After a certain amount of tin has been found dissolved in the batch I remove the undissolved parts of the tin by straining before depositing the batch into the containers.

I have found, however, that considerable time is required to obtain dissolved an amount of tin salts from imbedded metallic tin, suificient to prevent erosion of the container after packing, and I, therefore, prefer to employ simple compounds of tin which are more easily dissolved. I have found that a crystalline stannous oxide of the formula SnO and a stannous hydroxide of the formula of Sn(OH)2 are especially suitable for my purpose, the former preferably used in acid batches, the latter preferably in alkaline.

I have also found that the stannous oxide commercially available in best chemically pure grade is not especially suitable for my purpose being rather insolubleand giving black suspensions comparable in appearance with so-called Indian ink. This is due apparently to a high percentage of colloidal tin, not or imperfectly oxidized, present in the commercial SnO. c. p. The commercial stannous oxide 0. p. represents a black fine powder, while the SnO I employ appears in lustrous bluish metallic crystals. I

a blue black precipitate occurs, which is carefully washed and dried to give approximately 32 grams dry SnO crystals.

Stannous hydroxide, to be used according to my invention is also best prepared directly for use. I prefer to prepare it as follows:

Dissolve 50 gm. stannous chloride c. p. in 200 c. c. of boiling tapwater. Add boiling hot 60 gm. trisodium phosphate dissolved in 600 c. c. of tapwater. A white precipitate of S n(OH)z will occur which will rapidly settle out, if the solutions used have been hot. The sediment may be strained off and dried carefully or may be used still moist as a white muddy paste.

After having described the preparation of the tin compounds, I prefer to employ, I will now describe their use by describing the preparation of an acid and an alkaline batch as used in dual tubes for production of a foaming jelly, for which the protective action of the tin salts proved particularly useful.

Acid batch.-Dissolve all acids, to be used in the batch, in the water to be used, add the SnO prepared as described above, and heat until it is dissolved. This solution is then added to additional water, gums, glycerin and the like required: e. g. dissolve 55 gm. boric acid, gm. citric acid and 40 gm. tartaric acid in 360 c. c. boiling distilled water, add 8 gm. SnO and boil until dissolved. Add 2000 c. c. more distilled water and add this to 200 gm. gum Karaya, rubbed into a paste with 1000 c. c. glycerin. An acid jelly results which will have'little or no tendency to attack the tin of the tube neither if uncoated, nor if imperfectly coated as for instance, with vulnerable petrolatum.

Alkaline batch.-In the same manner as in the acid batch the tin compound used is nrst dissolved in a concentrated alkaline solution, and this solution then added to the balance of the batch. It is known that stannous hydroxide is highly sensitive against heat and alkali and .easily transformed into a black mixture of colloidal tin and stannous oxide by these factors. I have found that these can be overcome by the presence of glycerin and by careful heating not over 70 C.: e. g. dissolve 340 gm. trisodium phosphate in 340 c. c. of hot distilled water and add to it 1200 c. c. of glycerin. Add to this stannous hydroxide sediment obtained by precipitating 15 gm. stannous chloride as described above. Heat to '70 C. until dissolved. Add to this 1000 c. 0. Water and gm. sodium bicarbonate and mix this solution with 160 gm. gum Karaya rubbed into a paste with 1000 c. c. glycerin. An alkaline jelly results which has little or no tendency to attack tin if filled into an uncoated tin tube or into a dual tube coatedwith vulnerable petrolatum.

The acid and alkaline batches, prepared as described above, contain tin salts in the approximate amounts of 1:500, the acid salts being stannous citrate, tartrate and the like, the alkaline salts chiefly being sodium stannite of the formula Sn(ONa) 2. The amount of tin incorporated is as large as the batches will dissolve, and I have found from practical experience that it will prevent erosions and perforations substantially completely. A smaller, percentage of tin salts employed, even as low as 1:2000, will give a protection also but to a lesser degree.

I have found that the method described above prevents erosion and perforations, 'sufiiciently for practical purposes. The protection is a. relative and not an absolute protection-but great enough and simple enough so as to ofier a decided advantage in the manufacture of corrosive contents packed in tin or tinned containers. For the use with dual tube, employing petrolatum for coating and sealing purposes, my invention is indis- 75 pensable and makes alone a stable production of reactive. dual tube products possible.

The procedure of incorporation of tin salts into other products and the amounts used will be dependent upon the chemical conditions present in each product, and it is obvious that changes may be made in the procedure described herein without departing from the spirit of my invention.

The addition of tin,' respectively tin salts, to pharmaceutical and even food products is favored by the fact that tin is absolutely harmless and even beneficial to the human system and further by the lack of color of these salts. The addition of tin to the batch before it is deposited in the container creates in the beginning a condition, which will prevail in ordinary batches after lapse of time, but this simple procedure prevents the damage and loss resulting from corroded or perforated containers.

The herein .described procedure has given satisfactory results and it will be obvious to those skilled in the art, after an understanding of my invention, to make changes and modifications within the spirit and scope of the invention, v

and it is therefore intended that all materials contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What I claim and desire to secure by Letters Patent is:

1. A method for preventing erosions and periorations in metalcontainers' comprising substantially saturating the material packed in the metal container with salts, corresponding to the salts vformed in time by the natural reaction'between the material and container.

2. Amethod for preventing erosions and perforations in tin containers comprising dissolving tin salts in a batch of material, and then packing the material in a tin container.

3. A method for preventing erosions and perforations in tin containers comprising substantially saturating a batch of material with pure stannous oxide, and then packing the material into a tin container.

4. A method for preventing erosions and perforations in tin containers comprising substantially saturating a batch of, material with stannous hydroxide, and then packing the material into a tin container. i

5. A method for preventing erosions and perforations in dual metallic tubes comprising adding stannous hydroxide to an alkaline batch of material in one tube and pure stannous oxide to an acid batch of material in the other tube.

6. A package comprising a metal receptacle containing material capable of reacting with the metal of the container to form metallic salts, said material originally containing a. sufflcient amount of such salts to substantially saturate the material.

7. In a method of the character described, substantially saturating a batch' of material with pure stannous oxide in the form of lustrous bluish metallic crystals and then packing said material'in a metallic container.

8. A method for preventing erosions and perforations in dual tube metal containers lined with petrolatum, comprising substantially saturating the material to be packed in the container with metallic salts, correspondingto the salts formed in time by the natural reaction between the material and container, and then packing the material in the, container.

CLAUSS BURKART STRAUCH. 

